This is the end of the preview. Sign up
to
access the rest of the document.

Unformatted text preview: e current in the resistor in the T-network is
magnitude of the current is ⁄ ( ⁄( . The Part (d) The negative sign of associated with the current determined in Part (c) indicate that the current
flows though R from the ground into the junction of the T-network. i 3 55:041 Electronic Circuits. The University of Iowa. Fall 2011.
Question 3 For the amplifier shown, determine (a) the ideal closed-loop voltage gain. (b) What is the
actual closed-loop voltage gain if the open-loop gain is
and the op-amp is otherwise
ideal? (c) What is the minimum open-loop gain such that the closed-loop gain is within 1% of the ideal?
(12 points) Solution
Part (a) For an ideal op-amp, and so that the circuit is a follower and . Part (b) With finite open-loop gain, there is a voltage difference ⁄
between the
and
Assuming
, an equivalent circuit that captures the voltages is shown in (a) below. (a) (b) Applying KVL around the loop shown in (b) gives Part (c) From part (b) we have This must be within 1% of the ideal case ( Solving yields ), or . 4 inputs. 55:041 Electronic Circuits. The University of Iowa. Fall 2011.
Question 4 Consider the follower shown below. Except for a finite open-loop gain
ideal. Derive an expression for the closed-loop gain. (8 points) , the op-amp is Solution
With finite open-loop gain, there is a voltage difference ⁄
between the
and inputs.
Assuming
, an equivalent circuit that captures the voltages is shown in (a) below. (a) (b) Applying KVL around the loop shown in (b) gives 5 55:041 Electronic Circuits. The University of Iowa. Fall 2011.
Question 5 Consider the current-to-voltage converter circuit shown. The current source has a finite
output resistance , and the op-amp is ideal except for a finite open-loop gain
. (a) Show that the
⁄(
input resistance indicated in the figure is given by
. (8 points) Solution
P art (a) Determining the input resistance is equivalent to determining the Thevenin equivalent resistance,
which we do as follows: turn off independent sources add a test voltage
and determine the resulting
⁄ . To turn off a current source,...
View Full
Document